1st off, Thank you Eli for writing something vaguely positive for a change.

One of the only remaining fields of UI design in which expressive depth is not yet forbidden is video game design.

You can't really compare video ui game design and functional app interfaces. Video games are art, so it makes sense for the ui to match the art style and aesthetic of a game. If facebook's ui went all steampunk i doubt you would be praising it, even though it might be perfect in the context of a game.